You must not be paying attention then, because many detractors have made the claim repeatedly. It would be funny if it wasn't clearly the result of a predictable feedback loop. I'm really not interested in skylining one particular individual, but if you are genuinely interested in understanding what is happening: pick any one of the many tech writers appearing in the multitude of obituary compilations, then pull up their twitter timeline and observe their increasingly venomous attacks on cryptocurrency over the years.
With regard to them being useless: that argument falls apart very quickly when challenged. Unless you actually believe that software agents won't cause a massive economic shift, and that a weaponized financial system is really a good thing that brings stability. As far as it being a "ponzi scheme", a pump and dump, a tulip mania, a beanie-baby fad, etc... Just look at the time scale for a big clue as to why such an argument is laughable.